A typical example of the superconductive wiring is reported by Yamanaka et al, in the paper entitled as "Techniques for Formation of Superconductive Wiring on Alumina Substrate", Electronic Parts and Materials , Aug. 1987, Vol. 26, No. 8, pages 89 to 92. According to the paper, the wiring strips are formed by sintering paste lines which are printed on an usual alumina substrate and a fine grained alumina substrate, respectively, and the paste is prepared by mixing a powder of an yttrium-barium-copper oxide into an organic vehicle. The wiring strips are directly printed on the usual alumina substrate and the fine grained alumina substrate, and no protective film is provided on the wiring strips. The usual alumina substrate is lower in purity than the fine grained alumina substrate, so that it is considered that a substantial amount of impurity atoms are contained in the usual alumina substrate.
However, a problem is encountered in the prior-art superconductive wirings in stability. Namely, the wiring strips tend to lose the superconductivity within relatively short time periods, and, for this reason, the propagation paths for electric currents are liable to be blocked in the wiring strips.
Moreover, as reported in the paper, the superconductivity is achieved for the wiring strips formed on the fine grained alumina substrate, but no superconductivity is observed for the wiring strips formed on the usual alumina substrate. Then, another problem is encountered in the wiring strips reported by Yamanaka et al in the substrate used.
It is therefore an important object of the present invention to provide the structure of a superconductive wiring which is fit for use for a prolonged period of time.
It is also an important object of the present invention to provide the structure of a superconductive wiring which allows the wiring strip to stay in the superconductivity regardless of the substrate used.